In order to meet the growing demand for wide-bandwidth high-speed mobile access, Long-Term Evolution Advance (LTE-Advanced) standard is brought out by a 3rd Generation Partnership Projects (3GPP). With regard to Long-Term Evolution (LTE), the core of LTE is maintained by the LTE-Advanced. On this basis, frequency domain and space domain are extended by a series of technologies to increase the utilization ratio of the frequency spectrum and increase the system capacity etc. One of radio relay technologies, namely the LTE-Advanced, is directed to extend cell coverage, reduce the cell that cannot by reached in communications, balance loading, transfer services in hot spots and save the transmission success rate of a User Equipment (UE). As shown in FIG. 1, some new Relay Nodes (RN) are added between an original base station (e.g. Donor-eNB) and the UE. These RNs are in radio connection with the Donor-eNB, and not in wire connection with a transmission network, wherein the radio link between the Donor-eNB and the RN is called a backhaul link, and the radio link between the RN and the UE is called an access link. Downlink data arrive at the Donor-eNB first, then are transmitted to the RN, and further transmitted to the UE via the RN. Uplink data arrive at the UE first, then are transmitted to the RN, and further transmitted to the Donor-eNB.
In order to configure resources of the backhaul link, an RN-dedicated Physical Downlink Control Channel (R-PDCCH), an RN-dedicated Physical Downlink Shared Channel (R-PDSCH) and an RN-dedicated Physical Uplink Shared Channel (R-PUSCH) are defined. Started from the OFDM symbols received from the RN, the R-PDCCH may be part of Physical Resource Blocks (PDB) in the sub-frame applied to backhaul link downlink transmission, or may be part of the OFDM symbols (as shown in FIG. 2) or all OFDM symbols in the sub-frame applied to backhaul link downlink transmission. The R-PDCCH is used for dynamically or semi-statically distributing R-PDSCH resources and R-PUSCH resources, wherein the R-PDSCH resources are used for transmitting downlink data of the backhaul link, and the R-PUSCH resources are used for transmitting uplink data of the backhaul link. The RN can monitor downlink assignment, uplink authorization and others indicated by the base station on the PDCCH, and realize transmission between the RN and the base station on a corresponding Physical Downlink Shared Channel (PDSCH) and Physical Uplink Shared Channel (PUSCH). The RN can also monitor downlink assignment, uplink authorization and others indicated by the base station on the R-PDCCH, and realize transmission between the RN and the base station on the corresponding R-PDSCH and R-PUSCH. At the same time, the RN indicates the downlink assignment, uplink authorization and others on the PDCCH, and realizes the transmission between the RN and the UE on the corresponding PDSCH and is PUSCH, so as to avoid the conflict between the transmission between the RN and the base station and the transmission between the RN and the UE.
It can be seen that the RN does not have a relay function when acquiring the downlink assignment and uplink authorization sent by the base station by monitoring the PDCCH, thus it cannot indicate the downlink assignment and uplink authorization for the UE on the PDCCH and perform communications between the RN and the UE, i.e., the UE cannot be accessed to the network via the RN. Only when acquiring the downlink assignment and uplink authorization sent by the base station by monitoring the R-PDCCH, the RN can indicate the downlink assignment and uplink authorization for the UE on the PDCCH so as to allow the UE to access the network via the RN. Therefore it is necessary to introduce a method to switch from monitoring the PDCCH to monitoring the R-PDCCH to enable the UE to access the network via the RN.